Modulation of reactive oxygen species by salicylic acid in Arabidopsis seed germination under high salinity.

Potential roles of salicylic acid (SA) on seed germination have been explored in many plant species. However, it is still controversial how SA regulates seed germination, mainly because the results have been somewhat variable, depending on plant genotypes used and experimental conditions employed. We found that SA promotes seed germination under high salinity in Arabidopsis. Seed germination of the sid2 mutant, which has a defect in SA biosynthesis, is hypersensitive to high salinity, but the inhibitory effects are reduced in the presence of physiological concentrations of SA. Abiotic stresses, including high salinity, impose oxidative stress on plants. Endogenous contents of H(2)O(2) are higher in the sid2 mutant seeds. However, exogenous application of SA reduces endogenous level of reactive oxygen species (ROS), indicating that SA is involved in plant responses to ROS-mediated damage under abiotic stress conditions. Gibberellic acid (GA), a plant hormone closely associated with seed germination, also reverses the inhibitory effects of high salinity on seed germination and seedling establishment. Under high salinity, GA stimulates SA biosynthesis by inducing the SID2 gene. Notably, SA also induces genes encoding GA biosynthetic enzymes. These observations indicate that SA promotes seed germination under high salinity by modulating antioxidant activity through signaling crosstalks with GA.